Row crop conditions in Kansas
At this point, all summer field crops around Kansas are entering into the final reproductive stages. Corn is the furthest along, but yields can still be affected by stress conditions in some cases, depending on the stage of maturity. For both soybean and sorghum crops, the next coming weeks will be critical in shaping the potential yield.
At the national level, the last USDA crop progress report documented a total corn production at about 13.8 billion bushels, which represents 28% more than the 2012 crop production. The average yield is predicted to be close to 155 bu/acre (32 bu/acre above 2012). Soybean follows a similar trend, with improvements in total crop production and yield per unit area (both 4% up as compared with 2012 growing season).
Corn status in Kansas
The most recent Kansas Agricultural Statistics Service crop progress report projected that almost 90% of the Kansas’ corn crop is at the dent stage, more than 1/3 (33%) of the crop is already mature, and 8% has been harvested. Overall, almost 40% of the corn crop in Kansas was classified by the USDA as good or excellent. As compared with last year, this grain-filling period was much more favorable for corn, evidenced as a lower proportion of the crop mature (33%) as compared with the 2012 season (84%).
Related to the growth stages, the dent stage (R5) will take place 40 days after silking, which varies with weather conditions. The grain is drying down, with a moisture content level around 50-60%. Past experience shows that when corn is in the dent stage, biotic or abiotic stress conditions (e.g. high temperature, drought, pests, hailstorm, etc.) can exert some impact on yields through final kernel weight (shortening the dry matter accumulation period). Thus, there is still a portion of the yield that remains to be determined in the coming weeks in many fields. The final kernel weight will be determined when the crop reaches full physiological maturity (maximum dry mass accumulation), which can be identified as the formation of the black layer.
The most important task from this point to the end of the season is to scout the fields for the presence of weak stalks and plan the harvesting procedure -- prioritizing corn fields with weak or broken stems.
Figure 1. Corn at black layer. Photo by Ignacio Ciampitti, K-State Research and Extension.
Soybean status in Kansas
In most of the areas of the state the soybean crop is reaching the last stages of the reproductive phase, ranging mostly from R4 to R7 stages. Kansas Agricultural Statistics reported 97% of soybean setting pods for the entire state. At the present, almost 50% of the soybean crop condition has been rated good or excellent. The senescence process, detected as yellowing in soybean fields, was progressing rapidly with the warm temperatures and dry conditions experienced during the last few weeks. Kansas Agricultural Statistics reported that 24% of leaves had dropped as of September 15 (8 percentage points less than this time last year).
A considerable proportion of the potential soybean yield will be determined in the upcoming weeks, between the full seed stage (R6) and the beginning of maturity (R7). The beginning of maturity is recognized when only one pod on the main stem organ reached mature color (e.g. brown color).
At this point of the season, any biotic or abiotic stress can still impact the seed size. As discussed in a previous Agronomy eUpdate (eUpdate No. 418, August 23, 2013), drought and heat can severely modify and change seed size expected at the end of the season. In that article, two possible scenarios were explored, assuming the same number of pods per acre and seeds per acre in both scenarios. Under favorable conditions producing large seeds (2,500 seeds per pound), the yield expected was more than 40 bu/acre. In an unfavorable environment resulting in small seeds (3,500 seeds per pound), if all the other factors -- number of pods per plant and seed per pods -- are kept constant, the yield expected was about 30 bu/acre. Thus, a 25% yield reduction or more can be expected simply from changes in the final seed weight.
Continue to scout your soybean fields for crop production issues. Lodging can be an issue for soybeans. Lodging can affect not only harvesting but also the late-season photosynthetic efficiency of soybeans, accelerating senescence, and promoting reductions in seed weight and yield.
Figure 2. Soybean at the full seed stage. Photo by Ignacio Ciampitti, K-State Research and Extension.
Sorghum status in Kansas
Kansas Agricultural Statistics projected that more than two-thirds of the sorghum crop in Kansas is at or beyond the coloring stage, only 4 percentage points more than at this time last year. Only 6% of the crop was reported at full maturity, 18 percentage points less than at this time last year. Almost 50% of the sorghum crop was classified as in good or excellent condition; while 20% was projected as a very poor or poor. Similar to soybean, a proportion of the potential sorghum yield remains to be determined in the next coming weeks.
One of the main late-season factors that affects sorghum yields in Kansas is the possibility of a killing freeze before maturity. An early freeze will reduce the final grain weight due to a cessation in the dry matter allocation to the grain. The only management practice to avoid this phenomenon is to use shorter-season hybrids and, if possible, earlier planting dates in environments prone to early freezes.
Continue to scout your sorghum fields for early identification of crop production issues, including lodging or bird feeding. Often the utilization of pre-harvest desiccation will help reduce the moisture content and will promote a more concentrated maturation and an earlier harvest time. Utilization of pre-harvest desiccants is recommended when the crop is fully mature (25-35% moisture content), which is the stage at which a desiccant will not affect yields. Applications before maturity could compromise the final yield. Information related to different products and waiting period can be found at: http://www.ksre.ksu.edu/bookstore/pubs/MF3046.pdf
Figure 3. Sorghum at the coloring stage. Photo by Ignacio Ciampitti, K-State Research and Extension.
Ignacio A. Ciampitti, Crop Production and Cropping Systems Specialist